Iraq has arrested more than 60 security force members, including 11 senior officers over Sunday's twin suicide bombing in the capital Baghdad.

Those arrested include the commanders of 15 checkpoints near to where the attacks took place.

The attack in which more than 150 people were killed and 500 injured was the deadliest in Baghdad for two years.

Correspondents say the scale of the bombings raised new questions over the competence of Iraqi security forces.

The BBC's Gabriel Gatehouse in Baghdad says it is not clear whether those arrested are accused of negligence or collusion.

However, he added, it seems to confirm what many people have suspected - that the security forces are susceptible to infiltration by insurgents or are just not up to the job.

Iraqi Foreign Minister Hoshyar Zebari said in a BBC interview that he wanted the UN to investigate external interference, accusing Syria of providing a safe haven for the bombers, which Damascus has denied.

A militant group linked to al-Qaeda, Islamic State of Iraq, said on Tuesday that it had carried out the attacks in a claim that could not be independently verified....